1. Field of the Invention
This invention relates to a magnetic recording control device which controls the frequency characteristics and record level of a signal to be recorded on a magnetic recording medium such as a magnetic tape, in accordance with the characteristics of the magnetic recording medium.
2. Description of the Related Art
Conventionally, in order to improve the quality of a reproduced image, a domestic video tape recorder (VTR) is provided with a recording current controller by which the recording current flowing through a recording head coil in the recording process is set to a level for obtaining a reproduced voltage of the maximum level. When a reproduced voltage of the maximum level is obtained in the reproduction process, the quality of a reproduced image can be improved. The recording current from which the maximum reproduced voltage is obtained is called the optimum recording current (ORC).
Even in VTRs of the same kind, the value of the ORC varies depending on the scattering of the characteristics of magnetic tapes anti magnetic heads. Owing to the time aging of magnetic tapes and magnetic heads, the change of the ORC also occurs. Furthermore, depending on the performance of a magnetic tape, the value of the ORC differs with the frequency of the recording signal.
In the prior art, therefore, considering causes of the scattering of the ORC, an average value of the ORC is previously obtained, and this average ORC is applied to all mass-produced VTR sets and magnetic tapes, so that video signals are recorded with a constant recording current irrespective of the performances of the used VTR and magnetic tape. In the reproduction of the recorded video signals, hence, there may arise a case where the optimum characteristics cannot be obtained, according to the performances of the used VTR and magnetic tape. In such a case, a reproduced image may be reversed or a predetermined S/N ratio may not be attained.
In order to prevent such phenomena from occurring, a recording current control device having the configuration shown in FIG. 1 has been proposed (Japanese patent Application Laid-Open HEI 2-187902 (1990)). In the proposed device, a test signal is recorded in advance of the recording process on a magnetic tape to which the recording and reproduction processes are to be done, and the voltage reproduced from the magnetic tape is measured, whereby the ORC is determined.
In FIG. 1, 71 designates a recording head for recording the signal used for the ORC detection, 72 designates a magnetic tape, 73 and 79 designate rotary transformers, 74 designates a record amplifier, and 75 designates a gain switching controller which conducts the gain switch control on the record amplifier 74. The reference numeral 76 designates a comparison/decision unit which compares a plurality of input DC potentials with each other and, on the basis of the comparison result, gives the gain switching controller 75 instructions for the gain setting, and 78 designates a reproduction head which reproduces signals recorded on the magnetic tape 72 by the recording head 71. The reference numeral 80 designates a preamplifier, and 77 designates a detector which smooths the output of the preamplifier 80 and converts it to a DC potential.
Next, the operation of the control device will be described. In the recording process, a signal which has been amplified by the record amplifier 74 is supplied through the rotary transformer 73 to the recording head 71 and recorded on the magnetic tape 72. This recording is conducted in several different recording currents in accordance with instructions from the gain switching controller 75. In the reproduction process, the signals recorded on the magnetic tape 72 are detected by the reproduction head 78, and supplied through the rotary transformer 79 to the preamplifier 80. The signals which have been amplified by the preamplifier 80 are supplied to the detector 77 which in turn detects the output signals of the preamplifier 80 to smooth them. The smoothed signals are sent to the comparison/decision unit 76. The comparison/decision unit 76 compares the potential levels of the plural input signals with each other to find the ORC.
The recording current control device can set the ORC in accordance with the performance of the kind of the magnetic tape selected from magnetic tapes of different performances, thereby in a reproduced image enabling a predetermined S/N ratio to be attained. However, the control device has a problem in that, since the test signal has a single frequency, video signals are recorded without considering the frequency characteristics of the used magnetic tape and therefore the frequency characteristics of the recorded video signal are scattered. Although the ORCs of various magnetic tapes and magnetic heads may be correctly determined, such ORCs are those for a single frequency. Therefore, it is impossible to measure a correct ORC for a frequency-multiplexed signal such as a color signal. As a result, the electro-magnetic conversion characteristics are scattered, causing reproduced images to be scattered in image quality.
Video signals are previously FM-modulated and then recorded on a magnetic tape, in order to facilitate the recording of their information signals on the tape. The recorded signals are reproduced by the reproduction head and then demodulated to be output as reproduced video signals. The reproduction head outputs and the reproduced video signals vary in level in accordance with their frequency band.
FIG. 2 is a graph showing the frequency characteristics of two kinds of magnetic tapes in which outputs of the reproduction head for reproduced FM signals vary in level in accordance with their frequency bands. FIG. 3 is a graph showing the frequency characteristics of the two kinds of magnetic tapes for demodulated reproduced video signals. From FIG. 2, it will be noted that the variation of the outputs of the reproduction head increases in level as the frequency becomes higher and the frequency characteristics of B tape is inferior to those of A tape. In contrast, from FIG. 3, it will be noted that B tape has inferior S/N ratio and superior frequency characteristics as compared with A tape because the level variation of video signals reproduced from B tape is small as compared with that of video signals reproduced from A tape. From the above, it will be noted that the frequency characteristics of reproduced video signals vary in accordance with the performance of a magnetic tape, and that A tape with the high performance has superior S/N ratio and inferior frequency characteristics.
When a video signal is corrected so that the side-band components produced in the FM modulation are emphasized and then recorded, a reproduced signal having improved frequency characteristics can be obtained. Therefore, in a conventional VTR, a video signal which has been corrected is recorded. The amount of this correction is fixed regardless of the kind of a magnetic tape, or set so as to conform to a normal magnetic tape or a magnetic tape having a low performance. As described above, however, the frequency characteristics vary in accordance with the performance of a magnetic tape, and, as the magnetic tape has the higher performance, the frequency characteristics of the output of a reproduction head become more inferior. Conventionally, therefore, when a video signal which is to be recorded on a magnetic tape having a high performance, the correction is insufficiently conducted. In order to solve this problem, the side-band components may be more emphasized when the magnetic tape has the higher performance, so that the video signal has more superior frequency characteristics, thereby further improving the quality of a reproduced image. When the same correction is conducted on a video signal which is to be recorded on a magnetic tape having a low performance, however, a reproduced image may be reversed or the S/N ratio may be lowered.
As described above, in the prior art, there is a problem in that the correction of the frequency characteristics is not conducted in accordance with the performance of a magnetic tape and therefore the best image quality for the magnetic tape cannot be obtained.